It has been found by others that the operation of the machines referred to in the opening paragraph can be significantly improved with the aid of high pressure water sprayed on to the material to be cut. Not only does the high pressure water enhance the cutting action of the picks, but it also serves to improve the environment by reducing the amount of dust that is liberated into the atmosphere during cutting. Water pressures of up to 60 bars have been found by others to yield good results. However, recent developments in the art indicate that pressures of between 200 and 2000 bars produce even better results. At pressures of around 1500 bars it has been found that pick life can be increased by a factor of about 10 to 20.
To provide water to the rotating drums of such machines at an intermediate pressure of 10 to 60 bars does not create serious technical problems. Systems are in operation in which water at such intermediate pressures is supplied to the rotating drum by means of booster pumps either mounted on board the cutting machine or at some distance away therefrom. In the context of conventional mining machines using high pressure water, on board booster pumps are either located on the chassis of the machines or are built into ranging arms adapted to raise and lower the cutting drum. However, to supply water to the cutting drum at high pressures, for instance pressures of more than 200 bars, creates a serious technical problem. The further the pump is located away from the cutting drum, the longer the length of hoses or pipes that have to be provided to convey the water to the cutting drum and therefore the more vulnerable the hoses become to damage from the environment, such as falling rocks and the like. It will also be appreciated that the higher the pressure of the water, the more damage could be done to both operating personnel and equipment, by water escaping from burst or leaking hoses. Furthermore, since the cutting drum rotates during use, and the nozzles thereon require a high pressure only during a part of each revolution of the drum, expensive water swivels and sequence valves are required for such systems.
Booster pumps located in the ranging arms of such machines offer the advantage that they are protected from falling rocks and the like and are concealed from operating staff, but they are mechanically complicated and suffer from the disadvantage that any water leakage could contaminate lubrication oil usually present in such ranging arms as such arms usually also house a gearbox or other drive means for driving the cutting drum. Furthermore, the maintenance of such pumps is complicated because of their location in the ranging arm and the need for expensive water swivels and sequence valves still exists.